Add invite request system and Gitea Actions CI/CD pipeline

Invite request feature:
- Public form to request an invite when INVITE_REQUEST_ENABLED=true
- Stores requests in new invite_requests DB table
- Emails admins on new request, emails requester on approve/deny
- Admin panel tab to review, approve, and deny requests
- Approval auto-creates invite code and sends signup link

CI/CD pipeline:
- Build & push Docker image to Gitea registry on release
- Auto-deploy to staging with health check
- Manual workflow_dispatch for production deploys

Also includes client layout/sizing improvements for card grid
and opponent spacing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/config.py

@@ -149,6 +149,9 @@ class ServerConfig:
     SECRET_KEY: str = ""
     INVITE_ONLY: bool = True
 
+    # Allow visitors to request an invite (shown on login page when invite-only)
+    INVITE_REQUEST_ENABLED: bool = False
+
     # Metered open signups (public beta)
     # 0 = disabled (invite-only), -1 = unlimited, N = max per day
     DAILY_OPEN_SIGNUPS: int = 0
@@ -203,6 +206,7 @@ class ServerConfig:
             ROOM_IDLE_TIMEOUT_SECONDS=get_env_int("ROOM_IDLE_TIMEOUT_SECONDS", 300),
             SECRET_KEY=get_env("SECRET_KEY", ""),
             INVITE_ONLY=get_env_bool("INVITE_ONLY", True),
+            INVITE_REQUEST_ENABLED=get_env_bool("INVITE_REQUEST_ENABLED", False),
             DAILY_OPEN_SIGNUPS=get_env_int("DAILY_OPEN_SIGNUPS", 0),
             DAILY_SIGNUPS_PER_IP=get_env_int("DAILY_SIGNUPS_PER_IP", 3),
             BOOTSTRAP_ADMIN_USERNAME=get_env("BOOTSTRAP_ADMIN_USERNAME", ""),